This invention relates to a spot scanning system which utilizes a multifaceted rotating polygon for deflection of the scanning cycles depositing information upon recording media at video rates.
Much attention has been given to various optical approaches relating to spot scanning techniques which involve the imparting of information by means of modulating radiated flux incident upon recording media. Galvanometer driven movements have been used to scan the flux across a document for recording its information content thereon. Such arrangements have included planar reflecting mirrors which are driven in an oscillatory fashion. Other approaches have made use of multifaceted mirrors which are driven continuously. Various efforts have been made to define the spot size in order to provide for an optimum utilization of the scanning system.
One such effort is that described in U.S. Pat. No. 3,675,016. The approach used was to make the spot size invariant and as small as possible by defining the dimensions of the focused beam so that only part, preferably half, of a mirror facet is illuminated during scanning. This teaching alludes to generalized techniques for assuring the constancy of the size of the aperture of a rotating mirror scanning system. By either illuminating several facets of the mirror or by directing light in a beam that is sufficiently narrow to assure that less than a full facet is the most that can ever be illuminated by the beam and limiting scanning to that portion of the rotary travel of the facet when such facet is illuminated by all of such light beam. However, such system apertures are dimensionally invariant because the dimensions of the rotating facets have no influence on such apertures.
While the system as described in U.S. Pat. No. 3,675,016 may have advantages over the prior art, nevertheless, various constraints must be imposed upon the spot size and other relationships of optical elements within the system which are not always desirable.
In copending U.S. patent application, Ser. No. 309,874, filed on Nov. 27, 1972, and assigned to the assignee of the present invention, a spot scanning system is provided which does not have constraints imposed upon the spot size and other relationships of optical elements within the system which are not always desirable. As taught therein, a finite conjugate imaging system may be in convolution with the light beam and the rotating polygon. A doublet lens, in series with a convex imaging lens between the light source and the medium provides such an arrangement. Additionally, a cylindrical lens is positioned in the optical path between the polygon and the scanned medium to compensate for runout and polygon facet errors which may be undesirable.
It is thus an object of the present invention to further improve spot scanning systems which may tolerate substantial runout or facet errors.
It is a further object of the present invention to provide a spot scanning system which utilizes a multifaceted rotating polygon for achieving transverse spot deflection.
It is yet another object of the present invention to provide a spot scanning system which maintains an effective uniform spot size along the transverse scan direction and within a depth of focus normal to the recording medium.
It is still another object of the present invention to provide a spot scanning system which utilizes a rotating polygon for scanning a spot over a recording medium such that angular rotation of the polygon is linearly related to the transverse direction at the recording medium.
It is also an objective of the present invention to provide a flying spot scanning system which includes as its optical imaging elements a cylindrical lens in convolution with an astigmatic lens.
Other objects of the invention will be evident from the description hereinafter presented.